1. Field of the Invention
The disclosed inventions provide modification of an independent reactive plasma machine to enable checking the validity of the program selection on this machine by means of a central computer. For example, the invention can be applied to reactive plasma etching machines in a semiconductor production line.
2. Description of the Prior Art
In the industrial-scale manufacturing of semiconductors, there are limitations in the performance characteristics of the work stations of independent reactive plasma machines. One cause of these limitations arises out of the fact that it is necessary for a human operator to select and launch a program on a machine, or even to load the machine with a batch of silicon wafers or slices. The operator only has to make one error, and the entire batch is lost: it is scrapped. Moreover, it may happen that the error cannot be identified at once, and this batch will then continue to be processed unnecessarily.
In the invention, it is sought to obtain the ability to ascertain whether the operator has made a mistake, and, if an error has occurred, to place the machine in error mode before the plasma operation has been started and save the batch, or else to immediately identify the batch to be scrapped.
Now, in one aspect of the automation of production lines, it is sought to manage all the machines of a production line by means of a central CAM (Computer Aided Manufacturing) computer. This computer tracks each batch to be processed. It should not only provide for the synchronization of the various operations for manipulating the batches of wafers, but also control all the manufacturing parameters of the machines.
Since this approach is a novel one, only the new manufacturing machines can be integrated into an automated environment such as this. In particular they have, for this purpose, the interfaces needed to communicate with the central computer according to a determined, even a standardized, communications protocol.
The older machines, designed from a viewpoint of autonomy, cannot be integrated by the user into an environment such as this: they have neither the basic software nor the necessary interfaces, and cannot be adapted to the communications protocol. Only the manufacturer of such a machine could carry out such a major and costly conversion. The manufacturer prefers to develop entirely new machines.
However, since the central computer for the management of a production line has to track a batch at each step of processing, the following procedure is followed:
an operating sheet is associated with each batch;
at a given step, for a processing of the batch by such an independent machine, the operator will provide the central computer with information on the identification number of the batch;
in return, the computer indicates the formula that has to be selected on the independent machine;
the operator selects the formula and loads the batch into the machine.
If the operator makes a mistake, the computer cannot check this (much less take action), and the batch will be lost.
Now, the operator may indeed:
make a mistake about the batch number,
make a mistake about the operating sheet,
make a mistake of selection on the machine,
when a batch is divided, for example between two trays, make a mistake about the tray to be loaded (for example, one and the same tray may undergo the same processing operation twice, and the other one will not be subjected to it).
In any case, the batch will be lost for manufacture. If the error is not detected immediately, it will be necessary to wait for the checks on the batches at the end of manufacture, which will make it possible to identify the batch to be scrapped. In practice, these human errors significantly reduce the output of the manufacturing line.
A first aim of the invention is to check the selection of the formula on an independent reactive plasma machine for example a machine for the plasma etching of silicon wafers, and more generally a machine using fluids, the flow of the fluids being controlled. A fluid is taken to mean a liquid, a gas or even solid particles conveyed by a liquid or gaseous flux.
In a machine for the plasma etching of silicon wafers for example, a formula consists in determining the different parameters that govern the etching cycles.
These chief parameters are:
the reactive gases which will form the reactive plasma in the etching chamber;
their respective flow rate;
their pressure;
the radio-frequency power to be applied, to cause the etching by reactive plasma;
the time of duration parameters;
the parameters determining the end of the etching cycle (the light intensity in the spectral lines chosen).
An etching cycle generally comprises the following phases:
1. The loading of a wafer into the etching chamber. PA0 2. The pumping of the gases PA0 3. The stabilization of the flow-rates and pressures of the reactive gases PA0 4. Plasma etching PA0 5. The pumping of the residual gases PA0 6. Removal of the wafer PA0 7. At the end of the processing of the batch: the cleaning of the vacuum chamber (repeat of phases 2 to 6) and/or purging of the gas lines with a neutral gas (N2).
Each gas container is controlled by a mass flow controller that opens the valve of the container to varying degrees, according to the command that it receives from the machine:
a command for complete opening or complete closing, in the purging phase;
a command for opening to x%.
At the end of the stabilization phase, which typically lasts 60 to 90 seconds, the machine makes a check on the flow-rate of the gases. In principle, this check is ended before the start of the plasma etching.
Each flow controller receives a flow-rate command from the machine and gives the machine the real flow-rate value. A flow controller therefore has a control input and a reading output, which are connected to the machine.
In practice, these are commonly analog input/output ports. Thus, an x flow-rate command will correspond to an analog voltage with an amplitude of x% of the supply voltage Vcc of the controller, received at the control input of the flow controller.
During the gas flow-rate checking phase, each flow controller therefore receives a flow-rate command, in practice an analog voltage of x% of Vcc. Each flow controller sends the value corresponding to the opening of the valve to its analog output, this value being the value of the real flow-rate that is read by the machine. The machine can thus ascertain that the gas is really circulating between the container and etching chamber.
Indeed, if the response (real flow-rate) is different from the flow-rate parameter in the formula selected by the operator, it means that the gas is circulating badly. The machine, which should make the response of the flow controller agree with the parameter of the selected formula before setting off the plasma etching process, then goes into error mode and removes the wafer from the chamber, and the operator unloads the batch or tray of wafers from the machine.
However, in a certain number of machines, it is necessary for this difference to be truly significant: for machines such as these having high tolerance values, an error of 10% or 20% for example may be tolerated.